DISEASE CHARACTERISTICS:

• Histologically confirmed colorectal cancer
• Unresectable metastatic or locoregional disease
• At least 1 measurable lesion outside a previously irradiated area or an area treated with physical devices (e.g., cryotherapy, laser, or thermoablation)
• No prior enrollment in EORTC-05963
• No symptomatic brain metastases

PATIENT CHARACTERISTICS:

Age:

• Over 18

Performance status:

• WHO 0-2

Life expectancy:

• Not specified

Hematopoietic:

• Neutrophil count greater than 2,000/mm^3
• Platelet count at least 90,000/mm^3

Hepatic:

• Bilirubin no greater than 2 times upper limit of normal (ULN)

Renal:

• Creatinine no greater than 1.5 times ULN
• No uncontrolled hypercalcemia

Cardiovascular:

• No overt cardiac disease

Pulmonary:

• No severe respiratory illness

Other:

• Not pregnant or nursing
• Negative pregnancy test
• Fertile patients must use effective contraception
• Male patients must use effective barrier contraception during and for up to 6 months after study
• No baseline diarrhea greater than grade I (must have less than 4 stools per 24 hours)
• No prior grade III or IV toxicity related to irinotecan
• No sensory or motor neuropathy with functional impairment
• No prior hypersensitivity to any study drug
• No other primary tumor except basal cell skin cancer or carcinoma in situ of the cervix
• No uncontrolled infectious or chronic disease
• No psychological, familial, sociological, or geographical condition that would preclude study

PRIOR CONCURRENT THERAPY:

Biologic therapy:

• No concurrent prophylactic growth factor therapy

Chemotherapy:

• At least 1 month since prior chemotherapy
• No prior irinotecan, fluorouracil, leucovorin calcium, and oxaliplatin as combination therapy
• Other prior therapy containing irinotecan and/or oxaliplatin allowed
• No more than 1 prior chemotherapy regimen for metastatic or locoregional disease
• Adjuvant chemotherapy considered first-line therapy if tumor relapsed within 6 months of completion of therapy

Endocrine therapy:

• No concurrent corticosteroids except for emergencies

Radiotherapy:

• See Disease Characteristics
• Palliative radiotherapy for bone lesion allowed except for disease progression

Surgery:

• See Disease Characteristics